California was shaken early Thursday as a series of earthquakes struck in quick succession, raising concern in the seismically active region.
The US Geological Survey (USGS) reported six tremors ranging in magnitude from 2.6 to 4.0.
The seismic activity began at 1:51am ET, when four quakes occurred within just two minutes.
These quakes, roughly 72 miles north of San Francisco, struck near the San Andreas Fault, a massive 800-mile tectonic boundary stretching from Cape Mendocino to the Salton Sea.
Scientists have said that this fault is considered overdue for a ‘Big One,’ a magnitude 7.8 earthquake or higher, making the recent activity closely monitored.
The Maacama Fault, running north of Santa Rosa up to Ukiah, experienced a 3.9 magnitude quake.
This parallel fault system adds complexity to the region’s seismic activity, with experts suggesting the events may be part of a swarm or aftershock sequence.
And the latest tremor, a 3.6 magnitude, was detected in Southern California around 9:50am.
Northern California was jolted early this morning as multiple earthquakes struck within a short time frame
An assessment from Michigan Tech University showed that people typically do not feel quakes with a magnitude of 2.5 or less.
Those from 2.5 to 5.4 are often felt but only cause minor damage.
Residents reported light shaking, but no significant damage or injuries have been reported.
Scientists have long kept a close eye on the San Andreas fault, fearing it could soon release a devastating earthquake.
A 7.8 magnitude tremor could cause roughly 1,800 deaths, 50,000 injuries and $200 billion in damages, according to the Great California Shakeout.
Based on historical trends, it’s estimated that the San Andreas causes a major quake every 150 or so years, and the last one was 167 years ago.
The vast majority of earthquakes result from the constant movement of tectonic plates, which are massive, solid slabs of rock that make up the planetary surface and shift around on top of Earth’s mantle — the inner layer between the crust and core.
As the tectonic plates slowly move against each other, their edges can get stuck due to friction and stress will build up along the edges.
The swarm of four earthquakes hit roughly 72 miles north of San Francisco. The seismic activity happened within just two minutes
When that stress overcomes the friction, the plates slip, causing a release of energy that travels in waves through the Earth’s crust and generates the shaking we feel at the surface.
A new study from Caltech in Pasadena warned that the next Big One could be even bigger than what was originally thought.
They studied a 7.7 magnitude earthquake that shook Myanmar in March along the Sagaing fault, which is known for being eerily similar to the San Andreas.
That earthquake ended up rupturing a much longer section of the fault than scientists expected, killing thousands and causing widespread damage.
‘Future earthquakes might not simply repeat past known earthquakes,’ said Jean–Philippe Avouac, co–author of the study.
‘Successive ruptures of a given fault, even as simple as the Sagaing or the San Andreas faults, can be very different and can release even more than the deficit of slip since the last event.
‘In addition, historical records are generally far too short for statistical models to represent the full range of possible earthquakes and eventual patterns in earthquake recurrence.’
The devastating earthquake hit Myanmar on March 28, 2025, killing more than 2,000 people and leaving 3,900 injured.
The quake occurred when a section of the Sagaing fault ruptured, causing widespread damage along a swathe of territory down the middle of the country, including Sagaing, Mandalay, Magway and Bago regions and Shan State.
In their new study, the Caltech team used satellite imagery of the Sagaing Fault’s motion to understand exactly what happened – and whether a similar incident could happen in California.
‘This earthquake turned out to be an ideal case to apply image correlation methods that were developed by our research group,’ said Solène Antoine, first author of the study.
‘They allow us to measure ground displacements at the fault, where the alternative method, radar interferometry, is blind due to phenomena like decorrelation [a process to decouple signals] and limited sensitivity to north–south displacements.’
Based on studies of previous tremors along the Sagaing fault, the researchers expected that the earthquake would occur on a 186–mile (300–kilometer) section of the fault, where no large earthquakes had occurred since 1839.
The satellite images confirmed that this was the case, but that the fault actually slipped along a total of more than 310 miles (500km).
The 310–mile section shifted by a whopping 9.8 feet after the quake.
